import RPi.GPIO as GPIO
import time, sys
pin=21
GPIO.setmode(GPIO.BCM)
GPIO.setup(pin,GPIO.OUT)

p=GPIO.PWM(pin,400)
p.start(0)
dc=10
# for i in range(40):
#     dc += 2
#     print("dc:",dc)
while True:
    p.ChangeDutyCycle(45)
#     time.sleep(0.3)
    
p.stop()
GPIO.cleanup()
